Autoimmune disease is a collective term of a disease that makes innate immune system (having an inherent role in detecting a foreign substance from outside such as pathogenic microorganism and in excluding it) function abnormally, i.e., the abnormally functioned immune system recognizes ingredients composing self-cells or self-tissues as foreign substance to allow autoantibody or self-reactive lymphocyte to constantly arise excessively, and thereby inflammation arises systemically or organ-specifically with the production of cytokine to lead to histologic damage.
Despite such a bad disease, however, until now there has not been therapeutic approach to exhibit some sufficient effect for treating autoimmune disease without severe side effect, except a few diseases such as rheumatoid arthritis. Accordingly, it has been strongly desired to develop a new drug for treating autoimmune disease with high therapeutic effect and high safety.
Recently, it has been found that Toll-like receptor (TLR), especially TLR7 is deeply involved in the pathology of autoimmune disease (Non-Patent Literatures 1 and 2). Thus, it is expected that a compound acting on TLR could selectively control the immunoreactions initiated from pathogenic microorganism, autoantibody, or self-reactive lymphocyte, that is, such compound acting on TLR is expected as a new medicament for treating autoimmune disease which can completely cure the disease. On the other hand, recent reports based on studies using model animals suggests that medicaments for treating autoimmune disease which have inhibitory effect to TLR9 could induce the reduction of the drug efficacy or the safety problem (Non-Patent Literatures 3 and 4).
As a medicament for treating autoimmune disease which has inhibitory effect to TLR, for example, chloroquine, hydroxychloroquine, and the like are known (Non-Patent Literature 5).